This is a 371 of PCT/FR99/01093 filed May 7, 1999.
The invention relates to a process for preparing emulsions of bituminous binder which can be used in all the applications of bitumen emulsions, including the construction and maintenance of the road surfaces as well as the construction and building industry.
The invention also relates to the emulsions prepared according to the process of the invention.
Emulsions of bituminous binder are conventionally prepared by mixing a dispersed phase and a dispersing phase in a suitable mixer. The dispersed phase can consist either of pure bitumen or of a bitumen mixed with a flux, a fluidizing agent and/or an elastomer, i.e. a modified bitumen. The dispersing phase comprises, in particular, water and various emulsifiers or surfactants. Examples of mixers which may be mentioned are colloidal mills and static mixers.
More generally, mixers which are suitable produce a shear of phases present during mixing.
As a variant, it is also known practice to add the surfactant or an additional surfactant to the dispersed phase.
When the surfactant used for manufacturing the emulsion is cationic or nonionic, the emulsion generally contains from 50 to 70% by weight of bituminous binder. When the surfactant used is anionic, the concentration of binder in the emulsion is typically from 50 to 65% by weight. The emulsions obtained from anionic surfactants are usually finer and more viscous than those comprising cationic surfactants.
According to the process of the prior art, it is possible, by varying the nature and amount of surfactant used, to control the stability of the emulsion, i.e. both its stability on storage and its stability with respect to breaking.
More specifically, it is known in the art that by increasing the amount of emulsifier, it is possible to slow down the breaking of the emulsion and to increase its stability on storage.
However, the amount of emulsifier added also has an influence on the particle size of the resulting emulsion and on its viscosity, such that, according to the prior art, a compromise must be accepted in order to optimize the rate of breaking of the emulsion, its viscosity and the properties associated with the fineness of the emulsion.
The process of the invention allows better control of the rate of breaking almost independently of the viscosity and the particle size distribution of the emulsion.
The emulsions of the invention have a higher viscosity than the emulsions of the same formulation obtained according to the processes of the prior art. Viscous emulsions are particularly desirable for certain applications, such as the preparation of surface dressings (chipseals) which need to be applied to roads with a high slope or a high crossfall (superelevation).
Unexpectedly, the inventors have realized that the process of the invention results in the preparation of emulsions which have a narrower size distribution of the droplets in the dispersed phase (referred to as the granulometric distribution hereinbelow) and thus a higher viscosity. The other advantages of the process of the invention will readily become apparent to a person skilled in the art on reading the present description.
More specifically, the process of the invention comprises:
a) the preparation of a concentrated primary emulsion containing a surfactant and at least 65% by weight in the case of an anionic emulsion, or at least 70% by weight in the case of the other emulsions, of bituminous binder, by mixing an initial aqueous phase and a liquid bituminous phase under the effect of a mechanical shear energy and in the presence of the said surfactant; and
b) the addition of an aqueous dilution phase to the said primary emulsion.
The emulsions prepared according to the process of the invention have a higher viscosity than that of a corresponding emulsion of the same formulation, obtained by mixing an aqueous phase and a bituminous phase under the effect of the same mechanical shear energy as used for the preparation of the primary emulsion. Generally, the viscosity is at least 20% higher than that of the corresponding emulsion.
According to the invention, the expression xe2x80x9cbituminous binderxe2x80x9d means direct distillation, de-asphalting or oxidized bitumens, in pure, fluidized or fluxed form. As is known, hydrocarbon-based binders can be fluidized with light petroleum solvents such as kerosene, and fluxed with oils from coal or from petroleum. Other examples of bituminous binders which may also be mentioned are acidic bitumens such as naphthenic acid derivatives. These same binders can be used in a form modified by adding one or more polymers, organic resins or recycled rubber crumbs.
The primary emulsion is prepared in a manner which is known per se by mixing, under shear, an initial aqueous phase with a liquid bituminous phase containing the bituminous binder, in the presence of a surfactant.
The mixing under shear can be performed in the conventional mixers used in the art for the preparation of bitumen emulsions. This type of mixture can be prepared using colloidal mills, turbomixers, pumps or the like or alternatively using static mixers.
When the mixing is carried out continuously, the aqueous phase and the liquid bituminous phase are introduced in proportions which allow direct production of the desired concentration for the primary emulsion.
The mixing can also be performed in a batchwise manner by gradual enrichment of the initial aqueous phase, maintained under mechanical stirring in a suitable mixer, with liquid bituminous phase until the desired concentration for the primary emulsion is obtained.
The primary emulsion can be a direct emulsion (oil-in-water emulsion) or a reverse emulsion (water-in-oil emulsion).
The temperature at which the bituminous phase is introduced into the mixer is sufficient to maintain the bituminous binder in the liquid state. A temperature above 100xc2x0 C. is generally necessary.
A person skilled in the art will take care to ensure that the primary emulsion does not start boiling when it leaves the mixer.
To this end, it is convenient to adjust the respective temperatures of the aqueous phase and the bituminous phase which have to be introduced into the mixer and, if need be, to carry out the mixing under pressure.
As a guide, a temperature between room temperature and 70xc2x0 C. is generally suitable for the initial aqueous phase.
The primary emulsion is either anionic (and in this case it is prepared in the presence of an anionic surfactant) or cationic (in which case the surfactant is cationic), or alternatively nonionic (when the surfactant is nonionic). Cationic emulsions are preferred in the context of the invention.
According to the invention, it is possible to envisage the preparation of any other type of primary emulsion, for example a primary emulsion prepared using a zwitterionic surfactant.
The surfactants which can be used according to the invention are those generally used in the art for the preparation of a bitumen emulsion and can be cationic, anionic, nonionic or zwitterionic.
The surfactant can be added to the initial aqueous phase, to the bituminous phase or partly to each of these two phases.
As a general rule, all of the surfactant is added to the initial aqueous phase. However, addition of all or some of the said surfactant to the bituminous phase during the preparation of the primary emulsion leads to a finer particle size of the primary emulsion, i.e. the average diameter of the droplets of the primary emulsion is smaller than when all of the surfactant is present in the aqueous phase.
The amount of surfactant which needs to be used during the preparation of the primary emulsion will readily be determined by a person skilled in the art depending on the final use for which the bituminous binder emulsion is intended.
However, as a guide, it may be noted that an amount of surfactant of less than 20 kg per tonne of primary emulsion is generally sufficient.
When the surfactant is cationic, an amount of surfactant of from 0.5 to 10 kg/t is normally suitable.
More generally, when measuring out the surfactant, a person skilled in the art will take into account the desired stability properties of the final emulsion, the desired rate of breaking and the nature of the surfactant.
However, it will be noted that, according to the invention, the surfactant can be included directly in the actual structure of the bituminous binder. This is particularly the case for acidic bitumens of the naphthenic acid type which comprise functions with emulsifying activity in their structure. In this case, the presence of an additional surfactant in one of the two phases is not necessary during the preparation of the primary emulsion. The addition of an organic or inorganic base to the initial aqueous phase is then sufficient.
The respective amounts of initial aqueous phase and bituminous phase to be mixed for the preparation of the primary emulsion depend on the desired concentration of bituminous binder in the primary emulsion.
When the primary emulsion is a cationic, nonionic or zwitterionic emulsion, the binder concentration in the primary emulsion is at least 70% by weight, preferably greater than 70% by weight, in particular between 72 and 97% by weight, better still between 75 and 97% by weight, for example between 80 and 95% by weight.
When the primary emulsion is anionic, the binder concentration in the primary emulsion is at least 65% by weight, preferably between 65 and 97% by weight, in particular greater than 70%, better still between 70 and 95% by weight, for example between 72 and 90%.
According to the invention, it is essential to dilute the primary emulsion by adding an aqueous phase.
The dilution essentially does not change either the particle size distribution or the average diameter of the droplets in the primary emulsion. In addition, it gives a direct emulsion (oil-in-water emulsion).
The addition of the aqueous phase can be carried out in a continuous or batchwise manner. Depending on the case, the process of the invention is carried out in a continuous or batchwise manner. The method used for carrying out the dilution is not essential according to the invention.
A simple way of carrying out the dilution while working continuously is to unite two convergent flows, one consisting of the aqueous dilution phase, the other consisting of the primary emulsion.
When the process is performed in a batchwise manner, the aqueous dilution phase is introduced into the primary emulsion which is kept stirring.
The temperature of the aqueous dilution phase is advantageously less than 100xc2x0 C., preferably less than 50xc2x0 C., for example between 18 and 25xc2x0 C.
In a particularly advantageous manner, the dilution is carried out immediately after formation of the primary emulsion (i.e. without intermediate storage of the primary emulsion), in which case it is advantageous to use the aqueous dilution phase to cool the primary emulsion, if necessary.
According to another embodiment of the invention, it is possible to store the primary emulsion before dilution. For this storage, it is essential to avoid excessively low temperatures which might result in the emulsion freezing (and thus breaking). Hence, a suitable storage temperature is between 70 and 95xc2x0 C., or higher, provided that the storage pressure is adapted to avoid boiling.
The amount of aqueous dilution phase which needs to be added depends on the desired binder concentration for the final emulsion.
Generally, when the primary emulsion is cationic or nonionic, the final binder concentration in the emulsion will be from 50 to 70% by weight, preferably from 60 to 70%.
On the other hand, when the primary emulsion is anionic, a final binder concentration in the emulsion of between 50 and 65% by weight will be preferred.
When it is desired to prepare a bitumen emulsion which has a high rate of breaking, it is recommended to select an aqueous dilution phase free of surfactant in order to carry out the process of the invention.
As a variant, the aqueous dilution phase of the invention can contain an additional surfactant. In this case, the rate of breaking is lower.
This surfactant can be anionic, cationic, nonionic or zwitterionic, provided that it is compatible with the surfactant of the primary emulsion.
It is also possible to modify certain characteristics of the emulsion, such as the stability of the emulsion, the rate of breaking and the viscosity, by addition of one or more other additional aqueous phases to the emulsion thus obtained, each additional aqueous phase containing one or more additional surfactants. In this case also, the condition of compatibility between the various surfactants must be ascertained.
The total amount of surfactant present in the emulsion is a parameter which has an influence on some of the properties of the emulsion, such as its stability. Consequently, the amount of additional surfactants will be adjusted depending on the final use of the emulsion.
Nevertheless, as a general rule, the total amount of surfactant will not exceed 20 kg per tonne of emulsion, and, in the case of cationic surfactants, will not exceed 10 kg/t.
When the emulsion of bituminous binder is intended for the maintenance of road surfaces, the final emulsion preferably contains from 0.05 to 1.5% by weight, better still from 0.1 to 1% by weight, of surfactant.
As additional constituents, the aqueous dilution phase, the initial aqueous phase and/or the liquid bituminous phase can contain the usual additives used in the art, and in particular various solvents and/or polymers such as those which promote the adhesion or xe2x80x9cbondingxe2x80x9d of the emulsion, i.e. the ability of the emulsion to come into contact with the bodies present, such as gravel and granulates.
Other additives are stabilizers, antifreezes, thickeners or natural or synthetic latices, which are preferably added to the initial aqueous phase or to the aqueous dilution phase.
Examples of synthetic latices are an SBS (styrene-butadiene-styrene) latex, an SBR (styrene-butadiene rubber) latex and a polychloroprene latex. It will be noted in this respect that the addition of latex to the aqueous phase is usually carried out during the use of unmodified bituminous binder.
When the dilution is obtained by addition of one or more additional aqueous phases, it should be understood that each of these phases can contain such additives.
The result of this is that one advantage of the process of the invention is that, by virtue of the dilution step, it is possible to give the final emulsion specific properties by addition of suitable additives. Such a freedom of operation was not possible in the case of the conventional preparation processes, in which all of the constituents of the emulsion are added initially.
According to another of its aspects, the invention relates to the emulsions prepared according to the process of the invention.
The invention also relates to a direct cationic emulsion intended for the preparation of surface dressings (chipseals), comprising less than 70% by weight of bituminous binder, characterized in that it has a breaking index of not more than 90 (as measured according to French standard NFT 66-017) and a granulometric distribution, defined by an average diameter of the droplets in the dispersed phase, of less than about 8 xcexcm and a standard deviation of not more than 0.32.
The emulsions of the invention can be used in a variety of industrial applications, such as the construction and maintenance of road surfaces and the building industry.
They can be used in particular for the preparation of surface coatings, attachment layers or curing layers, surfacings, emulsion base courses, bituminous slurries or cold-cast surfacings, or alternatively to ensure the leaktightness of foundations.
According to the process of the invention, it is possible to independently control the particle size of the emulsion and the viscosity (or the particle size distribution). The reason for this is that, according to the invention, the viscosity of the final emulsion depends mainly on the concentration of bituminous binder in the primary emulsion, whereas the nature and amount of surfactant contained in the primary emulsion mainly have an influence on the particle size of the emulsion.
In addition, the process of the invention allows improved control of the rate of breaking, independently or almost independently of the amount and nature of the emulsifier initially present in the primary emulsion. This control is achieved by adding additional surfactants or stabilizers to the aqueous dilution phase.
Another advantage of the process of the invention is that it leads to an increase in the production capacity of conventional emulsion manufacturing plants on account of the final dilution.
Finally, it will be noted that the process of the invention can be carried out on conventional plants designed for the manufacture of bitumen emulsions by means of minor modifications to allow the dilution of the primary emulsion.
The emulsion of the invention can be stored before use. It will preferably be maintained at a temperature of between 20 and 70xc2x0 C. Advantageously, the emulsion is stored at a temperature from 40 to 50xc2x0 C. by insulating the storage containers.